Method of forming heat transmissive wall surface

ABSTRACT

A plurality of extremely fine grooves are formed on one side of a heat transmissive wall, and there are also provided a plurality of fine second grooves which are substantially parallel and closely adjacent to each other and which cross the first-said grooves. Fine notched ribs are formed between said second grooves, with the end portions thereof being rubbed and stretched transversely and connected to the adjoining ribs.

United States Patent [1 1 Kakizaki et al.

[451 Sept. 23, 1975 METHOD OF FORMING HEAT TRANSMISSIVE WALL SURFACE[75] Inventors: Kimio Kakizaki; Takashi Suzumura,

both of Hitachi, Japan [73] Assignee: Hitachi Cable, Ltd., Japan [22]Filed: Feb. 1, 1974 [21] Appl. No.: 438,613

[52] US. Cl. 29/1573 A; 29/l57.3 R; 29/4703; 113/118 A; 165/133 [51]Int. CL B21D 53/02; B23P 15/26 [58] Field of Search. 29/1573 R, 157.3 A,157.3 B, 29/DIG. 23, 470.3; 113/118 A, 118 R;

[56] References Cited UNITED STATES PATENTS 3,454,081 7/1969 Kun et al.165/133 Szumigala 165/133 X Zatell 29/1573 B Primary Examiner-C. W.Lanham Assistant Examiner-D. C. Reiley, III Attorney, Agent, orFirm-Craig & Antonelli [5 7 ABSTRACT A plurality of extremely finegrooves are formed on one side of a heat transmissive wall, and thereare also provided a plurality of fine second grooves which aresubstantially parallel and closely adjacent to each other and whichcross the first-said grooves. Fine notched ribs are formed between saidsecond grooves, with the end portions thereof being rubbed and stretchedtransversely and connected to the adjoining ribs.

11 Claims, 2 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of 23,906,604

US Patent S cpt. 23,1975 Sheet 2 of2 3,906,604

HEAT FLOW RATE q(KcoL/n1 h) -5 5 l l l I l 2 3 5 7 IO 2o DEGREE OFOVERHEATING TS C) BACKGROUND OF THE INVENTION In order to accomplisheffective heat transmission from the surface of a plate, pipe' or suchinto a liquid contacted therewith, such as for example liquid nitrogen,liquid oxygen, alcohol, water or thelike, it has been proposed toroughen the surface ofthe plate, etc., by providing a porous layer ofpulverized metal on said surface.

Such roughened wall surface produces a number of active boiling spotsthroughout the surface layer so that the heat transmitting ortransferring efficiency is mark- .edly improved as compared with thewall which is merely provided with fins or the like to enlarge thesurface area. Howevenin such heat transmitting wall, the flow(convection) of the liquid that promotes heat transfer is limited to acertain locality and hence it is impossible to obtain an overall heattransmitting effect. Further, if some impurities, such as oil, areincluded in the liquid, the fine pores communicating with one another inthe layer may be clogged, inviting reduction of the heat transmittingefficiency.

SUMMARY OF THE INVENTION The present inventors have previously proposeda heat transmissive wall provided on one side thereof with a pluralityof extremely fine voids arranged substantially parallel toeach other andcommunicated with the outside through small pores. Such wallconstruction permits substantial rectification of the entire liquid byvirtue of fine voids and ensures perfect retention of vapor, resultingin even more enhanced heat transmitting efficiency than obtainable withthe wall providecl with a porous layeron its surface.

The presentinvention proposes a method whereby such improved heattransmissive wall can be obtained.

According to the present invention, such improved heat transmissive wallcan be obtained by providing extremely small ribs between the finegrooves formed on one side of the wall and connecting the ends of saidribs with the adjoining ribs.

More specifically, the method of the present invention features thefollowing steps: firstly amultiplicity of fine first grooves and amultiplicity of similar fine sec ond grooves crossing said first groovesand arranged substantially parallel and closely adjacent to each otherare formed on one side of aheat transmissive wall, and then the'ends ofthe small notched ribs formed between i said second grooves arefrictionally rubbed and stretched transversely and connected to'theadjoining zribs. j

The term heat transmitting or transmissive wall used here refersgenerically to the walls of the pipes, plates and the like which aremade of copper, alumi num or other good heat conductive metals.Therefore, "the small voids formed in such wall may be of any suitableconfiguration such as linear, helical or ringshaped, and the groovesthat provide such voids may be formed by any known method such ascutting or rolling. In case of employing cutting, it is preferred to usea plow-up type cutting method that causes deforma {tion as in plowingup, rather than a method which causes cut-off. Such cutting work can beaccomplished with ease by selecting a cutting edge of a suitableconfiguration and by adjusting the cutting speed.

Of the fine grooves formed in such way, the first grooves become thecutouts in the small ribs formed between the second grooves. They alsoserve as minute through-holes in the upper walls of the small voidswhich are formed by the succeeding frictional working. They willtherefore become useless if they are eliminated or worked off duringsuch frictional working, so that it is desirable that each of the firstgrooves is provided with a certain suitable width in its inlet opening.In certain applications of the heat transmissive wall, said minutethrough holes formed in the grooves in the above-described way may bediminished in their ser-. viceability. In such cases, the first groovesmay be formed concentrically in certain localities.

The second grooves formed crossing the first grooves are the parts thatbecome the small voids created by deformation of the small ribs formedbetween the adjoining second grooves. It is therefore desirable thatthese second grooves are somewhat deeper than the first grooves, buttheir width may be small in comparison with their depth.

The ends of the small ribs formed between the second grooves withformation of such grooves are frictionally worked and stretched. in thetransverse direction and connected to the adjoining ribs at a middlepart. Such frictional working may be accomplished, for instance, byusing a method employing a wire brush or roll rotated at high speed inpressed contact with said rib ends. Thethus worked small rib ends aresoftened or fused and stretched laterally to adhere fast to a middlepart of each adjoining rib, thus forming a wall well resistant to theboiling pressure in the formed small voids. The wall surface is alsomoderately roughened thereby to give rise to a number of boiling spots.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a photograph, magnified 50times, of a part of the surface of a heat transmissive pipe obtainedaccording to an embodiment of the method of the present invention; and

FIG. 2 is a graph showing the heat transmitting characteristics of saidheat transmissive pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there isphotographically shown on a 50 -times magnified scale, a part of thesurface of a heat transmissive pipe obtained'by working the surface of acopper pipe according to the method of the present inventionfiTherelatively large dark parts seen sporadically on the surface indicatethe minute through-holes formed in the upper walls of the small voids.This surface has been obtained by performing knurling, cutting and wirebrushing successively in that order.

The knurling was accomplished in the following way. A knurling unitprovided with a fine knurling wheel or a roll formed with a plurality ofhelical closely adjacent knurling ridges is secured to a side of thetool rest of a lathe, then said roll is pressed against the surface of acopper pipe fixed at one end to the chuck of the lathe before practicingthe cutting of the second grooves, and then said copper pipe is rotatedwhile moving the tool rest along the lead screw.

This knurling work has produced on the surface of said copper pipe aplurality of fine grooves which are inclined at the angle of 45relativeto the axis of the pipe and which are continuous helically and closelyadjacent to each other. These fine grooves are the first grooves.

It is desirable that these first grooves have the depth within the rangeof about 0.05 to 0.3 mm and exist with density of less than 1mm pitch.

In the surfaceshown in the photograph of FIG. 1, there were formed theV-shaped grooves with depth of 0.15 mm and density of 0.5 mm pitch.

The cutting was practiced after formation of said first grooves bypressedly attaching a grooving cutter mounted at the other side of thetool rest against the revolving copper pipe and moving the tool restlittle by little along the lead screw. The cutting was of the type inwhich the copper pipe surface is not cut off but deformed.

This cutting work has produced on the pipe surface a plurality of finegrooves which cross the above-said first grooves and which arecontinuous helically and closely adjacent to each other, as well as aplurality of fine ribs separated by said second grooves and each beingformed with a small V-shaped notch along a part extending from the endto a middle point.

"These second grooves preferably have a depth equal to or greater thanthat of the first grooves and exist at density of less than 1 mm pitch.

The ribs formed with formation of the second grooves are necessarilyextremely small in size, but as they are formed by deformation of thepipe surface by the cutting work after the fashion of plow-out, the endsthereof project out more from the pipe surface than before the cuttingwork. Therefore, the depth of the second grooves after the cutting workis greater than the depth of cut by the grooving cutter.

In forming the surface seen in FIG. I, the cutting .work has beenperformed with the depth of cut of 0.4 mm and at density of 0.4 mmpitch.

The thus formed second grooves crossed the first grooves at the angle ofabout 90and presented a continuous helical configuration with depth of0.76 mm, while the fine ribs formed simultaneously had thickness ofabout 0.2 mm and projected 0.58 mm from the surface of the copper pipe.The ends of these ribs were tapered.

The wire brushing that succeeded the above-said formation of grooves waspracticed by removing the copper pipe from the lathe upon completion ofthe grooving work and passing said pipe through a brushing unit. Thebrushing unit comprises a plurality of wire brush wheels arrangedradially along the passage of the copper pipe so that they will contactthe entire periphery of the passing pipe and also adapted to berotatable at high speed and movable back and forth relative the axis ofsaid passage. Arrangement is also made such as to allow movement of thecopper pipe at a constant speed. It is of course possible to makearrangement such that the copper pipe is fixed stationary while the wirebrush wheels are movable.

Each wire brush wheel is adjusted such that its outer periphery willcontact a circle slightly smaller than the outer diameter of the fineribs formed on the copper pipe, and when said copper pipe is passedthrough its passage, the end portions of the ribs are frictionallyrubbed successively by the high-speed rotating wire brushes and softenedand deformed by the friction heat that develops resultantly, wherebysaid end portions of the ribs are stretched thinly and laterally withoutcut off.

Consequently, the end of the thinly stretched copper film is pressedagainst and connected to a middle part of each of the adjoining ribs toclose the second grooves, and small voids or cavities continueshelically and communicating with the outside through small notchedthrough-holes are formed below the thin copper film. The surface of thethin copper film constituting the upper walls of said voids and thesurface of the heat transmissive pipe is roughened to present anintricate ruggedness as seen in FIG. 1. Although the small through-holesformed in accordance with the numerical figures of the first grooves arecomplicated and not constant as seen in FIG. 1, their size is within therange of 0.06 to 0.4 mm

In FIG. 2, the curve shown by a double-dotted chain line expresses theheat transmitting characteristics of the heat transmissive pipe having asurface such as seen in FIG. 1. It is obvious that these characteristicsare far superior to those of the flat surface shown by the solid line,those of the finned surface shown by the broken line and those of theporous layer covered surface shown by the single-dotted chain line inFIG. 2. Such excellent heat transmitting characteristics are ascribed tothe presence of the above-said fine voids.

If a high-temperature object is placed in the heat transmissive pipe ofthe present invention and then immersed in a liquid, the small voids arefilled with the liquid passed thereinto through the through-holes, andthe liquid which entered said voids is immediately heated and boiled toproduce bubbles. Since the small voids are arranged continuouscircumferentially, a substantial portion of the bubbles rise up in thevoids in the form as they are or while growing, and eject out in theform of microscopic vapor bubbles from the upper small through-holesinto the liquid enveloping the heat transmissive pipe. As a result, thebubbles are reserved, though transiently, in the voids, whereby thebubbles are reduced to the thickness of the extremely thin liquid filmpresent between the void walls through-out most of the heat transmittingdistance, and also intrusion of the liquid into the voids from the lowerthroughholes is induced to cause a voluminous flow in the entire liquid,thus allowing accomplishment of very effective heat exchange.

The above-said results are obtained when the heat transmissive pipe isused by positioning it horizontally. In case the pipe is used in avertical state, the described characteristics are somewhat deteriorateddue to, for one thing, the tunnel effect of the voids. In such a case,it is desirable to form the fine voids parallel to the axis of the pipeor with a slight inclination thereto, and a heat transmissive pipehaving such voids can be shaped in the same way as described above.

While the foregoing description concerns a heat transmissive pipe, theabove-said change of characteristics also holds true with a heattransmissive plate. Shaping of a heat transmissive plate requires moretime and labor than for the pipe, but such shaping will be greatlysimplified and expedited by improving the groove forming tools andapparatus.

According to the present invention, as apparent from the foregoingexplanation, a plurality of fine grooves are formed on one side of aheat transmissive wall to provide a number of boiling spots, and theends of the small ribs formed between said grooves are frictionally,

rubbed and connected to the adjoining ribs, so as to form the voidswhich permit reservation of bubbles effective for heat transmission andwhich are also useful for rectifying the liquid flow, whereby there canbe obtained a splended heat transmissive wall which is far effectivethan a wall provided with a porous layer on its surface. Further, sincethe small through-holes communicating the interior of the voids with theoutside are formed simultaneously with formation of the voids byutilizing the previously formed grooves, the working involved is simpleand easy and no void deformation takes place, and thus there can beobtained a highquality heat transmissive pipe at high efficiency.

What is claim is:

l. A method of forming a heat transmissive wall surface comprising thesteps of forming a plurality of fine first grooves on one side of a heattransmissive wall, while forming a plurality of fine second grooveswhich cross said first grooves and which are substantially parallel andclosely adjacent to each other, then frictionally heating by rubbing andstretching transversely the ends of the small notched ribs formedbetween said second grooves and fusingly connecting said ends to theadjoining ribs.

2. The method according to claim 1, in which the respective grooves areformed by rolling, and frictional rubbing of the rib ends isaccomplished by wire brush- 3. The method according to claim 1, in whichsaid respective grooves are formed by cutting, and frictional rubbing ofthe rib ends is accomplished by wire brush- 6 ing.

4. The method according to claim 1, in which the first grooves areformed by rolling and the second grooves by cutting, and frictionalrubbing of the rib ends is accomplished by wire brushing.

5. The method according to claim 2, in which the first grooves areformed by knurling.

6. The method according to claim 3, in which the second grooves areformed by a cutting method which does not cut off the wall surface butdeforms it.

7. The method according to claim 4, in which the second grooves areformed by a cutting method which does not cut off the wall surface butdeforms it.

8. The method according to claim 5, in which the second grooves areformed by a cutting method which does not cut off the wall surface butdeforms it.

9. The method according to claim 1, in which continuously extendingcavities are formed within the surface by said step of fusinglyconnecting said ends of the ribs between said second grooves, .saidcavities communicating with the exterior of the surface by through-holesformed by said first grooves.

10. The method according to claim 9, in which said second grooves have adepth equal to or greater than that of said first grooves.

11. The method according to claim 9, in which said cavities effect flowof a liquid therein from respective lower through-holes to respectiveupper through-holes, thereby enhancing heat exchange from the heattransmissive wall to said liquid.

1. A method of forming a heat transmissive wall surface comprising thesteps of forming a plurality of fine first grooves on one side of a heattransmissive wall, while forming a plurality of fine second grooveswhich cross said first grooves and which are substantially parallel andclosely adjacent to each other, then frictionally heating by rubbing andstretching transversely the ends of the small notched ribs formedbetween said second grooves and fusingly connecting said ends to theadjoining ribs.
 2. The method according to claim 1, in which therespective grooves are formed by rolling, and frictional rubbing of therib ends is accomplished by wire brushing.
 3. The method according toclaim 1, in which said respective grooves are formed by cutting, andfrictional rubbing of the rib endS is accomplished by wire brushing. 4.The method according to claim 1, in which the first grooves are formedby rolling and the second grooves by cutting, and frictional rubbing ofthe rib ends is accomplished by wire brushing.
 5. The method accordingto claim 2, in which the first grooves are formed by knurling.
 6. Themethod according to claim 3, in which the second grooves are formed by acutting method which does not cut off the wall surface but deforms it.7. The method according to claim 4, in which the second grooves areformed by a cutting method which does not cut off the wall surface butdeforms it.
 8. The method according to claim 5, in which the secondgrooves are formed by a cutting method which does not cut off the wallsurface but deforms it.
 9. The method according to claim 1, in whichcontinuously extending cavities are formed within the surface by saidstep of fusingly connecting said ends of the ribs between said secondgrooves, said cavities communicating with the exterior of the surface bythrough-holes formed by said first grooves.
 10. The method according toclaim 9, in which said second grooves have a depth equal to or greaterthan that of said first grooves.
 11. The method according to claim 9, inwhich said cavities effect flow of a liquid therein from respectivelower through-holes to respective upper through-holes, thereby enhancingheat exchange from the heat transmissive wall to said liquid.